This invention relates generally to the field of variable geometry turbochargers and, more particularly, to an improved vane design for a plurality of pivoting aerodynamic vanes disposed within a turbine housing of a variable nozzle turbocharger to provide improved vane operation and extended vane/turbocharger service life.
Turbochargers for gasoline and diesel internal combustion engines are devices known in the art that are used for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft and housed in a compressor housing. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the turbine housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
In a turbocharger it is often desirable to control the flow of exhaust gas to the turbine to improve the efficiency or operational range of the turbocharger. Variable geometry turbochargers have been configured to address this need. A type of such variable geometry turbocharger is one having a variable exhaust nozzle, referred to as a variable nozzle turbocharger. Different configurations of variable nozzles have been employed in variable nozzle turbochargers to control the exhaust gas flow. One approach taken to achieve exhaust gas flow control in such variable nozzle turbochargers involves the use of multiple pivoting vanes that are positioned annularly around the turbine inlet. The pivoting vanes are commonly controlled to alter the throat area of the passages between the vanes, thereby functioning to control the exhaust gas flow into the turbine.
In order to ensure the proper and reliable operation of such variable nozzle turbochargers, it is important that the individual vanes be configured and assembled within the turbine housing to move or pivot freely in response to a desired exhaust gas flow control actuation. Because these pivoting vanes are subjected to millions of high temperature cycles during turbocharger operation it is necessary that any such pivoting mechanism be one that is capable of repeatably functioning under such cycled temperature conditions without enduring any cycled temperature related material or mechanical problem or failure.
Known multiple vane variable nozzle turbochargers include vanes that are each configured having a shaft projecting outwardly therefrom, each such shafted being positioned within a respective shaft opening in a turbine housing or nozzle wall. While the vanes are commonly actuated to pivot vis-a-vis their shafts within the respective openings, it has been discovered that such conventional vane attachment and pivoting mechanism is not without its problems.
For example, in order to ensure freely pivoting movement of the vane shaft with the opening it is essential that the shaft project perfectly perpendicularly from the vane, to thereby avoid undesired binding or otherwise impairment of the vane pivoting movement. Secondary straightening or machining operations are sometimes necessary to ensure the perpendicularity of the vane shafts., which secondary operations can be both time consuming and costly. Additionally, this type of vane attachment and pivoting mechanism can produce a high cantilevered load on the vane shaft when actuated that can also impair free vane pivoting movement, and that can ultimately result in a vane material or mechanical failure.
It is, therefore, desirable that a vane pivoting mechanism be constructed, for use with a variable nozzle turbocharger, in a manner that provides improved vane operational reliability when compared to conventional vane pivoting mechanisms.
A variable geometry turbocharger incorporating the present invention includes a turbine housing having an inlet for exhaust gas and an outlet, a volute connected to the inlet, and an integral outer nozzle wall adjacent the volute. A turbine wheel is carried within the turbine housing and attached to a shaft. A plurality of vanes are disposed within the turbine housing, each vane having a hole extending into the vane through an axial vane surface substantially parallel to the outer nozzle wall, each vane hole receiving a respective post projecting outwardly from the outer nozzle wall, the vanes further having actuation tabs extending from an axial vane surface opposite from the holes. An annular unison ring is positioned axially adjacent the vanes, the unison ring having a plurality of slots that each accommodate a respective tab therein. Te unison ring is rotated to effect movement of the tabs within respective slots by pivoting movement of the vanes on the posts, wherein such movement of the tabs within the slots causes the vanes to move radially relative to the turbine wheel shaft.